Homeostasis

Introduction

The term “Homeostasis” was given in 1926 by Walter Bradford Cannon. Homeostasis is derived from two Greek words ὅμοιος (homios) i.e., similar and στάσις (stasis) i.e., standing still. It is a self-regulating process that maintains consistency in internal, physical, and chemical conditions. This sets the optimal condition for the functioning of organisms. When optimal conditions are already present, homeostasis is maintained by the natural resistance to change. Homeostasis is a state of dynamic equilibrium; thus continuous change occurs while uniform conditions prevail.

Examples of homeostatic regulation include control and coordination done by the electrical circuits, the nervous system, and by the hormonal system.

Why is Homeostasis Required?

Homeostasis is important for the survival of organisms mostly to resist changes in the constantly changing environment. It involves the regulation of the internal environment which is required to sustain life. Along with body temperature being an important factor, homeostasis is useful to regulate-

• pH

• The concentration of glucose, and

• The concentration of various ions like sodium, potassium, calcium, etc.

Regulation of Homeostasis

Regulation of homeostasis is dependent on the following factors which are again interdependent −

• Receptor − It is the component used for sensing. It detects the changes occurring in the external and internal environment. It responds to external and internal environmental changes.

• Control centre/Integration centre: Processes information received from the receptors.

• Control centre/Integration centre− Processes information received from the receptors.

• Effector − It responds to the commands given by the integration centre. It can be used to either enhance or suppress the stimulus.

For example − Maintaining temperature of the body is done in the following manner:

Process

When there are changes in the outside temperature, the skin receptors detect them and transfer this information to the brain. In the brain, this information is processed and the effector gland or organ is signalled to carry out response to the stimulus. Hence, if the temperature outside is high then the brain signals the blood vessels to dilate (vasodilation) which in turn reduces body temperature. Along with vasodilation sweat glands release sweat, which helps in reducing body temperature. If the temperature outside is low, then vasoconstriction (vessels constrict) occurs which prevents heat from being lost from the body.

Factors Affecting Homeostasis

The following factors affect homeostasis −

• Sugar level - If a rise in the sugar level takes place it is stored in other parts of the body to be used later in some complex form. If the sugar level decline mechanisms are present to break down the complex substances stored to restore the level.

• Osmotic pressure - The movement of water from low solute concentration to high solute concentration is important to maintain cell pressure.

• Temperature - The body maintains 36.6O-37.2O C temperature. This is done by the hypothalamus gland.

• Genetic composition - The DNA expression is altered according to the environment. This is tightly regulated to maintain the internal environment.

• Physical condition - The pH, fluid balance, oxygen tension, etc., are all maintained for homeostasis.

Body Systems and Homeostasis

Body systems play a crucial role and actively participate in the maintenance of homeostasis. Each body system have various controlling mechanisms which contribute to homeostasis. The endocrine and nervous systems are the main body systems that help to maintain homeostasis.

Examples

Formed elements in blood −

• Platelets - clotting

• RBCs - transportation of gases

• WBC’s- defence mechanism

Endocrine glands and hormones

• Nervous system

• Plasma

• Nutrients - cellular metabolism

• Hormones - messengers

• Salts - metabolic activity and buffer.

Mechanism of Homeostasis

Physiological Mechanism

• Negative feedback mechanism − If the level of a component is too low, the body comes up with ways that increase the concentration of that component, and similarly, if the level of any component is very high, then the body tries to bring it down. Hence the term negative feedback.

  Example − Maintaining blood sugar levels in humans. Increased blood sugar levels are detected by the nervous system. Cells of the pancreas release insulin to lower the glucose levels in the blood. If the level of blood sugar decreases, the hormone glucagon is released by cells of the pancreas to increase the level of blood sugar. Hence homeostasis is maintained.

  Maintenance of blood calcium levels inside the body is also an example of a negative feedback mechanism.

• Positive feedback mechanism −In contrast to the negative feedback mechanism, the positive feedback mechanism enhances the initial stimuli. This type of mechanism is usually found to push a reaction towards completion.

  Example − During childbirth positive feedback mechanism is used. When a child is ready to be delivered, neurons pass on signals to the brain, which commands the pituitary gland to release the hormone oxytocin. This oxytocin helps in increasing uterine contractions and also exerts pressure on the cervix. This in turn causes a release of more oxytocin and thus stringer uterine contraction finally leading to the expulsion of the baby.

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Morphological Mechanism

Morphological homeostasis limits the extent to which genetic and/or environmental variation is translated into phenotypic variation, providing generation-to-generation fitness advantage under a stabilising selection regime.

Behavioural Mechanism

It is the tendency of an organism to maintain homeostasis by exhibiting a behavioural means to maintain it.

Example − Temperature regulation by shivering in cold weather.

Examples of Homeostasis

• Body temperature regulation

• Blood calcium level regulation

• pH homeostasis

• Respiratory gases homeostasis

• Body water level homeostasis

• Blood pressure homeostasis

• Blood oxygen level homeostasis

• Maintenance of sodium concentration

• Maintenance of potassium concentration.

Conclusion

• Homeostasis is the property that helps to maintain constant internal, physical, and chemical conditions in the body.

• It is required to resist changes occurring and helps the organism to survive.

• Various factors influence homeostasis in the body such as genes, temperature, sugar level, osmolarity, etc.

• Many mechanisms such as physiological, morphological, and behavioral mechanisms are required to maintain homeostasis.

FAQs

Q.1. Where are receptors present in the body to maintain body temperature?

Ans. Changes in the external temperature can be detected by the receptors which are present on the skin. These are also known as thermoreceptors.

Q.2. What happens in case of failure of homeostasis?

Ans. Failure of homeostasis results in illness or diseases. Even death or disability is possible in severe cases. It makes the person feel uneasy and cannot perform daily activities easily.

Q.3. What are ectotherms and endotherms?

Ans. Ectotherms are those organisms which cannot maintain their body temperature with differing environmental temperatures and endotherms ate those organisms which can maintain their body temperature with differing environmental temperatures.

Q.4. Which organs play an important role in the homeostasis of blood glucose levels?

Ans. The liver is the organ that plays an important role in maintaining blood glucose levels. It also includes organs of the digestive system, as here the carbohydrates are broken down and absorbed.

Q.5. State various receptors involved in maintaining homeostasis?

Ans. Receptors detect changes in the external environment and send signals to the brain. Various receptors include −

• Photoreceptors - They respond to light stimuli.

• Thermoreceptors - They detect changes in the temperature.

• Olfactory receptors - They detect stimulus coming in the form of smell (odour or fragrance). They are located on the epithelium of the nose.

• Auditory receptors - They detect stimulus coming in the form of sound waves and are located in the organ of Corti in the ear.